The invention relates generally to an information-containing carrier in which the information is recorded in a plurality of tracks, each of which includes a unique information or address code identifying each specific track of recorded information.
Information carriers of this type known to the prior art have the information recorded by means of magnetic, optical, thermal or electrical characteristics of the carrier. The present invention is applicable to all carries having such characteristics and is not restricted to the particular configuration of the carrier; that is, the carrier may be in the form of a disc, a card or plate, a drum, cylinder, tape or other geometry.
In known information carriers access to a particular track containing information desired is accomplished in several ways. One of these causes the reading apparatus to automatically move in discrete steps from one information-containing track to the next adjacent track and to detect the unique identifying address for each particular track. Only when the desired track is reached will the reading apparatus stop and convey the information contained thereon.
In a different system the reading apparatus is caused to move rapidly in jumps of a predetermined number of tracks and after each jump to read the address and compare it to the desired track. When the difference between the desired track address and the actual track address being read is different than the predetermined number, then the apparatus moves from track to track sequentially until the desired track is reached.
In yet a different system voltage comparison or other physical measurement means is utilized for determining the position of the desired information as compared to the position of the apparatus reading the information from the carrier.
In still a further system the reading apparatus is caused to quickly move from a first position to a second position through a distance equal to a number of tracks. The number of tracks through which the movement occurs is determined by taking the difference between the address position of the reading device and the address of the track desired. As movement occurs, the tracks passed are counted until the desired number of tracks have passed, at which point in time the reading device is caused to stop and then enter a fine search phase similar to that first above described prior to locking onto the desired track.
The fastest access time to a desired track which is available by any of the known systems is on the order of a few seconds. The best prior art known to applicant is shown in U.S. Pat. Nos. 3,931,457 and 4,106,058.